Differential/WAAS/EGNOS, TomTom, & GPSSlim?

Quantum · Posted: Mon May 29, 2006 9:01 pm Post subject:

I don't trust SiRFDemo, after all the grief it's caused with the Holux 236.

I can now confidently report that Holux's util, GPSView, does not actually switch on WAAS/EGNOS, as we had suspected.

The good news is that I've found a utility that does, and which works with the Holux 236 via bluetooth. I have an IPaq4700 running WM2003SE.

The util is SiRFTech. I should warn you though, that this utility is like playing with fire. If you are careless, you will be sorry.

You'll connect to Com8 at 38400. After using each tab in the util, you have to close it, which is a little weird. Once running, check the NEMA tab, and make sure you get live data. Then switch to SiRF mode, staying at 38400. This will take a couple of tries on the 236 (as it does with all other pods). Once NEMA seems dead, close it and open the SiRF tab.

You will notice that the data is now filled in in each SiRF tab, and that Static Navigation is off in the 236 from the factory, which is a Good Thing(TM). If you choose, turn on SBAS (WAAS/EGNOS). Again, do not fiddle with anything else, unless you would like to have a heart attack. Be sure to switch back to NEMA, if you want TomTom to actually work. This may take a couple of tries.

I will now drive around with this turned on and see if I get my WAAS birds. I doubt I'll notice accuracy difference in TomTom, but unless there's an obvious problem, I am leaving WAAS on. All the inaccuracy reports are on EGNOS, and they find that in fact one EGNOS bird is worse but one is better. Since WAAS is used for munitions and aircraft landing in the US, my theory is that it should be an improvement over nothing.

It seems I have the older 3.1.0 firmware. I guess there's no way to upgrade this without their fscking cable which I'm not going to buy.

Now, here's the eye-opening article on the effectiveness of EGNOS in Paris.

The effectiveness of EGNOS was quite different between the two birds there, one making things worse, and one better.

But more startling is the accuracy of the Nemerix chipset, when compared with the dizzy wandering of SiRF3. I thought we had the best chipset, but nope.

Thanks again to Skippy. If he hadn't taken the time to help, I would not have brought this info back to y'all.

elyl · Posted: Mon May 29, 2006 9:17 pm Post subject:

Just a quick question about the GPSlim cable - I assumed it was just a standard USB-to-miniUSB connector like I have for my digital camera/PPC/MP3 player, but I look on their website, and their cable's got a weird dongle thing in the middle of it. Is it a specially wired cable for the GPSlim, or can I just use a standard USB cable? I tried connecting the GPS to my computer via USB when I first got it, but couldn't get XP to recognise and install it, even using the software on the GPSlim CD.

mikealder · Posted: Mon May 29, 2006 9:23 pm Post subject:

The 236 does require the special cable to transfer data between itself and the PC, contact Holux for the cable, you can use a standard cable but only for charging the device - Mike

Quantum · Posted: Mon May 29, 2006 9:25 pm Post subject:

Right, it's what's called a 'soap-on-a-rope'. It converts USB to serial, and buffers it down to the CMOS levels that the pod requires. The pod is serial CMOS, not serial RS232 or USB.

Quantum · Posted: Tue May 30, 2006 1:01 am Post subject:

Drove around Seattle today with WAAS enabled + running GPSView, and just about everywhere I went, I saw WAAS 35. (This is one of the two WAAS satellites for the US) Never saw 47 though. (The other one)

However, I only ever saw 35 as a red outline bar in GPSView, never as a blue bar as with the other 10 GPS satellites in the sky I usually get here.

Why would it give me only a red outline bar, even though it gives signal strengths over 40, which is as high as most other birds here? Needless to say, I never got a DGPS 3D lock.

At this stage, I have invented what seems to be a new thing to science; achieving WAAS on the Holux 236, and actually seeing one of the WAAS satellites, but unfortunately I have not yet locked its almanacs.

We are on the cutting edge here, peoples...

Skippy · Posted: Tue May 30, 2006 11:34 am Post subject:

Greenglide · Posted: Tue May 30, 2006 11:34 am Post subject:

Unfortunately just because TomTom may be given more accurate information doesnt, necessarily, mean it will KNOW that it is more accurate.

This would not, therefore, sole the OPs problem which I suspect was due to his home setting not being on a road on the map so TT didnt calculate a correct route to it. Rolling Eyes

Quantum · Posted: Tue May 30, 2006 8:38 pm Post subject:

Yes Greenglide, this is what I've said several times. Nevertheless, it is doubtful that WAAS is worse than a poke in the eye with a sharp stick.

I guess I am stuck, at this point. I only ever get the red-outlined bar in GPSView, which tells me WAAS is not being actually used. The bird is visible all over town, but something's wrong. I've left it sit for 8 hours, and no improvement.

I suspect it is one of the DGPS parameters, but I can not find a reference anywhere describing what these parameters are, nor advisable settings for them. These are not made generally available I guess, to keep the shoe salesmen form mucking up their GPS, but ironically those who are technically-proficient, cannot safely set the parameters, without knowledge.

The settings I'm thinking of in particular are:
- DGPSSource|InternalBeaconFreq (Is 0 some acceptable default, or does it -disable-?)
- DGPSSource|InternalBeaconBitRate (Should this be 10, or 50?)
- DGPSMode|DGPSSelection (presumably should be Auto)
- DGPSMode|DGPSTimeout (Is this when it stops looking for WAAS birds? 18 seconds is too short. And is this after Hot, or Cold restart?)
- SBAS|SBASPRN (Which of the WAAS birds provides ionospheric data, the largest cause of error?)
- SBAS|SBASMode (Seems that 'Testing' is most forgiving, as Integrity throws out non-verified WAAS data)
- SBAS|Timeout (Presumably should be Default)

I am also interested in:
- ModeControl|TrackSmoothing (unchecked)
- And the lowest elevation WAAS is allowed to work at, which I suspect is ElevationMask|NavigationMask (now 5, which is fine, if this is what I think it is)

I can't even find out WTF a 'DOP' is. I'd like to know about setting DOPMask|DOPSelection.

Now, a shoe salesman would go ahead and try these settings without study, but I sure am not.

If you think that I shouldn't know this, just because I don't, just stow it, Buford.

Mikeact · Posted: Tue May 30, 2006 11:21 pm Post subject:

Terribly sorry, but, does it make the slightest bit of difference when navigating home or anywhere else ?

Quantum · Posted: Tue May 30, 2006 11:38 pm Post subject:

Mikeact, please read my first post on the first page of this thread. Again, that is what triggered this. And as I say, yes, TT snaps to the road, and yes, the Sirf3 chipset skates all over the place, and yes, they are getting worse results from one of the EGNOS satellites. (although the other gives better, than no DGPS, as I'd annotated above)

But I believe that WAAS is tweaked in, because it is used for munitions and aircraft in the US. It has been in operation longer than EGNOS. If TomTom gets an inaccurate reading from the pod, it sure won't improve on it. And there is a good chance that WAAS will improve accuracy, which will translate through. I am willing to take that risk. It is better than a poke in the eye with a sharp stick.

It seems that I am annoying people here, with my investigations. Maybe I should stop the updates. Less information is better, is it? Jeez, I'd thought I was performing a service...

Skippy · Posted: Wed May 31, 2006 12:52 am Post subject:

Quantum · Posted: Wed May 31, 2006 8:32 pm Post subject:

OK, I've got it now. And fixed a few other stability/accuracy things too.

So don't worry about me any more.

Robin2 · Posted: Wed May 31, 2006 9:20 pm Post subject:

Skippy · Posted: Wed May 31, 2006 11:43 pm Post subject:

Robin2 · Posted: Thu Jun 01, 2006 12:39 am Post subject:

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